1. Field of the Invention.
The present invention relates generally to engine cooling systems for skid steer loaders. In particular, the present invention is a flexible cooling system which can utilize a single fan to draw fresh air through the radiator, and to evacuate dust, debris and engine-heated air from the engine compartment.
2. Description of the Prior Art.
Skid steer loaders are compact, highly maneuverable vehicles which are commonly used in a variety of applications. Maneuverability of skid steer loaders is enhanced by a favorable weight ratio for the weight carried at the front and rear axles during loaded and unloaded conditions. It is desirable to provide as compact a vehicle structure as possible to maximize the efficiency of this weight ratio. Accordingly, known skid steer loaders have an engine compartment located at the rear of the vehicle immediately behind the operator's compartment. Approximately 70% of the vehicle weight thereby overlies the rear axle when the bucket at the front of the vehicle is unloaded.
Due to the extremes in environments and operating conditions to which skid steer loaders are often subjected, durable and high capacity engine cooling systems are required. Skid steer loaders are frequently used in locations where considerable air borne debris, dust and other contaminants are present. Contaminant concentration is typically greatest near the surface on which the loader operates, and decreases at greater distances from the surface. However, the engine compartment in skid steer loaders is usually positioned relatively low on the vehicle, near the surface where contaminant concentration is greatest.
The engine compartment of a skid steer loader is typically located immediately behind and sometimes extends underneath the operator's compartment. Unless provisions are made to evacuate engine-heated air from within the engine compartment, temperatures within the operator's compartment can become uncomfortable. However, if too much air is evacuated from the engine compartment, contaminants will be drawn in through various randomly located openings. This dust and debris will accumulate within the engine compartment, reduce cooling system efficiency, and result in other problems.
A variety of engine cooling systems have been utilized in skid steer loaders, and are disclosed generally in the Henline et al. U.S. Pat. No. 4,117,90 and the Mather et al. U.S. Pat. No. 4,535,868. In one prior art design, the radiator and oil cooler are mounted between a louvered rear closure and an engine fan. The engine fan draws air from outside the vehicle through the radiator and oil cooler. While cooling systems of this type can provide adequate cooling for the engine, no provision is made for evacuating heated air from within the engine compartment. As a result, the operator's compartment can get hot, providing an uncomfortable working environment for the operator. Furthermore, the large mass of air passing through the radiator and oil cooler is drawn from locations near the surface. Dust and debris therefore build up within the engine compartment and reduce cooling system efficiency.
Another engine cooling system uses a fan driven by a hydraulic motor to pull ambient air through an intake radiator and oil cooler located near the top of the engine compartment. Although less debris is drawn into the engine compartment, this system does nothing to alleviate uncomfortably high temperatures which can develop in the operator's compartment.
In still other known cooling systems, air is drawn through louvers into the engine compartment by a radial fan, and directed out of the engine compartment through the radiator and oil cooler. While this system has the advantage of evacuating heated air from the engine compartment thereby reducing the temperature in the operator's compartment, it is not without its drawbacks. Dust and dirt drawn into the engine compartment by the fan is blown into the radiator and oil cooler, thereby decreasing their efficiency.
Another problem associated with the above-described cooling systems relates to the design constraints imposed upon designers. A relatively large mass of air must be drawn through the restrictions of the oil cooler and radiator. In general, the larger the engine used in the loader, the greater the air flow needed to adequately cool it. With a line of skid steer loaders having differently sized engines it can therefore be difficult to provide the optimum balance between fan size, blade configuration and fan speed in order to minimize fan horsepower consumption and noise while at the same time maximizing the mass of air transmitted.
It is evident that there is a continuing need for improved cooling systems for skid steer loaders. A cooling system which draws ambient air through the radiator and oil cooler, and which evacuates heated air from within the engine compartment, is desired. The system should evacuate only sufficient air from the engine compartment to maintain a stable near ambient condition so as to minimize the amount of debris carried into the engine compartment. Air drawn through the radiator and oil cooler should be as free of contaminants as possible. The system must, of course, be efficient. It should also be flexible enough to be capable of being adapted to a variety of different loader models having differing system demands.